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A pixel detector asic for dosimetry using time-over-threshold energy measurements
Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
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2011 (English)In: Radiation Measurements, ISSN 1350-4487, E-ISSN 1879-0925, Vol. 46, no 12, p. 1619-1623Article in journal (Refereed) Published
Abstract [en]

In this work we present the design of a chip which provides the readout of a highly segmented diode array, in which signals induced by individual X-ray photons are processed discretely. There are several benefits to this approach, including the ability to achieve a high signal to noise ratio due to the inherently low sensor capacitance, and the suppression of background noise (e.g. dark current) using an analogue threshold. The segmentation also ensures a linear behaviour even at very high dose rates. A time over threshold (ToT1) energy measurement technique provides an immediate digital value corresponding to the energy deposited onto the diode by each individual photon. Deadtime-free operation is achieved by reading out a subset of the detector segments at a time while the rest of the detector continues to process signals. This paper describes the application-specific integrated circuit (ASIC) chip which was designed to provide pre-processing of photo-induced signals in the detector and readout of the processed digital data.

Place, publisher, year, edition, pages
2011. Vol. 46, no 12, p. 1619-1623
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:miun:diva-15827DOI: 10.1016/j.radmeas.2011.06.061OAI: oai:DiVA.org:miun-15827DiVA, id: diva2:488888
Available from: 2012-02-02 Created: 2012-02-02 Last updated: 2017-12-08Bibliographically approved
In thesis
1. A Hybrid Pixel Detector ASIC with Energy Binning for Real-Time, Spectroscopic Dose Measurements
Open this publication in new window or tab >>A Hybrid Pixel Detector ASIC with Energy Binning for Real-Time, Spectroscopic Dose Measurements
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Hybrid pixel detectors have been demonstrated to provide excellent quality detection of ionising photon radiation, particularly in X-ray imaging. Recently, there has been interest in developing a hybrid pixel detector specifically for photon dosimetry. This thesis is on the design, implementation, and preliminary characterisation of the Dosepix readout chip.

Dosepix has 256 square pixels of 220 mm side-length, constituting 12.4 mm2 of photo-sensitive area per detector. The combination of multiple pixels provides many parallel processors with limited input flux, resulting in a radiation dose monitor which can continuously record data and provide a real-time report on personal dose equivalent. Energy measurements are obtained by measuring the time over threshold of each photon and a state machine in the pixel sorts the detected photon event into appropriate energy bins. Each pixel contains 16 digital thresholds with 16 registers to store the associated energy bins. Preliminary measurements of Dosepix chips bump bonded to silicon sensors show very promising results. The pixel has a frontend noise of 120 e-. In low power mode, each chip consumes 15 mW, permitting its use in a portable, battery-powered system. Direct time over threshold output from the hybrid pixel detector assembly reveal distinctive photo-peaks correctly identifying the nature of incident photons, and verification measurements indicate that the pixel binning state machines accurately categorise charge spectra. Personal dose equivalent reconstruction using this data has a flat response for a large range of photon energies and personal dose equivalent rates.

Place, publisher, year, edition, pages
Mid Sweden University, 2012. p. 238
Series
Mid Sweden University doctoral thesis, ISSN 1652-893X ; 128
Keywords
Hybrid pixel detector, low power readout chip, photon counting, time over threshold (ToT), energy binning, active personal dosimeter (APD)
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:miun:diva-16171 (URN)978-91-87103-20-9 (ISBN)
Public defence
2012-05-30, O102, Mittuniversitetet, Campus Sundsvall, Sundsvall, 13:00 (English)
Opponent
Supervisors
Available from: 2012-06-07 Created: 2012-05-03 Last updated: 2012-08-01Bibliographically approved

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Wong, Winnie S.

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